Docs: Add category to ability registration in README

[karthikeya-io]

Related issues #135

• This PR adds the category field to the ability registration example in the README, as it is a required parameter.

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.25%. Comparing base (8d0f1ef) to head (e1daf0c).

Additional details and impacted files

@@            Coverage Diff            @@
##              trunk     #169   +/-   ##
=========================================
  Coverage     88.25%   88.25%           
  Complexity     1243     1243           
=========================================
  Files            54       54           
  Lines          4035     4035           
=========================================
  Hits           3561     3561           
  Misses          474      474           

Flag	Coverage Δ
unit	88.25% <ø> (ø)

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